Automatic transmissions in relatively large mobile machines often include a hydrodynamic retarder or hydraulic retarder that is associated with the output of, or input to, the transmission. When employed, hydraulic retarders utilize relative rotation of components within the retarder to assist in slowing the machine. The hydrodynamic retarder converts energy from the driveline into heat, which is then typically dissipated using the transmission oil cooling system.
Heat generated within the hydraulic retarder is dependent upon pressure developed with the hydraulic retarder. Flow into and out of the hydraulic retarder is sometimes controlled by respective valves. U.S. Pat. No. 7,527,338 B2 to Long, et al., discloses a hydromatic retarder control apparatus. The apparatus uses a retarder multi-function valve and a retarder regulator valve to provide flow to a flow valve and on to the retarder, lube cooler from a fluid pump, and return flow from the retarder.